Football supporters' groups yesterday called for a tightening of the Premier League's rules over the ownership of clubs in the wake of Alexandre Gaydamak's £15m bid to become co-owner of Portsmouth. They claimed that the league's recently toughened "fit and proper person test" for directors is little more than a requirement to sign a form - and that a new package of measures on the way clubs are run is required.

The rules were strengthened in August 2004, partly in response to pressure from the government's football task force.

Malcolm Clarke, chairman of the Football Supporters' Federation, said: "The football authorities deserve some credit because the rule is better than it was two or three years ago, but it is basically a self-declaration and not as strong as we would like. There is no investigation - and if someone signs up and says they are a decent chap, it is taken at face value. We would like to see it strengthened and are canvassing our members at the moment about amendments."

Phil French, the chief executive of Supporters Direct, said: "The fit and proper persons test is a positive step in the right direction in terms of accountability, but I think many supporters would want it to go further in terms of firmly establishing the financial integrity of major new investors. However, this would inevitably throw up more questions in terms of what level of resources of expertise would be required and how it could be policed without a change in company law."

Concern has been raised over the move by the 30-year-old son of the Russian billionaire Arkady Gaydamak to become an equal partner in the Fratton Park club with the chairman Milan Mandaric. While Gaydamak Jr has an unblemished business record, details of his background and his wealth are shrouded in uncertainty.

Many believe his father is the driving force behind the proposed deal, despite his loud denials. He is the subject of an international arrest warrant issued by the French police over an Angolan arms-for-oil scandal in the 1990s.

If the deal goes through and Alexandre Gaydamak becomes a director, he will be required to sign a declaration, confirming he has not been convicted of a range of offences, including fraud and theft.

The league believes the declaration would act as a serious deterrent to those who have something to hide, but acknowledges it does not have the investigative expertise and resources of bodies such as the Financial Services Authority.

A spokesman for the Premier League said: "The fit and proper persons test means that any new director has to declare if he has been convicted of a number of offences, as well as meeting other requirements. It is part of a range of measures that augment UK company law and demonstrates that the professional game is, and expects to be, run to a high standard of corporate governance."

Clarke added: "We would like a wider package of controls on the way clubs are governed. We need to look at the increasing trend for foreign ownership with Chelsea, now Portsmouth and the Glazers at Manchester United."

The "fit and proper person test" will also be examined as part of a European-wide football inquiry instigated by the sports minister Richard Caborn. A spokesman for the Department of Culture, Media and Sport said: "There is a need across Europe to look at a single standard for a fit and proper person to be involved in football that everyone can sign up to."